Thong seams digging into my crotch

My first thong was a Doreanse thong in medium and it's a great fit. I bought a Jockey thong in medium wore it for a day and that thing was in my crotch felt like a saw blade cutting my balls off slowly. I figured it was the wrong size, so I sized up to a large and still the same problem but not as painful. What do I do?